Valves are commonly used in process control systems to control the flow of process fluids. Sliding stem valves (e.g., a gate valve, a globe valve, a diaphragm valve, a pinch valve, etc.) typically have a closure member (e.g., a valve plug) disposed in a fluid path. A valve stem operatively couples the closure member to an actuator that moves the closure member between an open position and a closed position to allow or restrict the flow of fluid between an inlet and an outlet of the valve. Additionally, to provide a desired and/or to achieve certain flow characteristics of the fluid, valves often employ a cage that interposes in the path of fluid between the inlet and the outlet of the valve. A cage can reduce capacity flow, attenuate noise, and/or reduce or eliminate cavitation. Additionally, a cage surrounds the closure member to provide stability, balance, and alignment to the closure member.
To effect a seal between a cage and a closure member, the closure member typically includes a channel or groove that receives a seal and/or piston ring that engages an inner surface of the cage. Typically, the size of the valve, industrial process conditions such as pressure conditions and operational temperatures (e.g., temperatures between −100° F. and 450° F., temperatures greater than 450° F. with the use of an anti-extrusion ring, etc.) of the process fluids are used to determine the type of valve and valve components that may be used such as, for example, the types of seals that may be used to effect a seal between a cage and a closure member. For example, a valve having a process fluid that experiences a relatively high pressure differential across its flow passageway typically employs a pressure-balanced closure member to minimize or reduce the thrust or force to be exerted by an actuator to move the closure member to a closed position. Additionally, valves having larger sized ports or flow passageways (e.g., greater than 1 inch in diameter) may employ spring-loaded seals to provide a tighter seal. Typically, a bidirectional seal assembly is often employed with pressure-balanced closure members to provide bidirectional sealing between the cage and closure member to minimize or eliminate leakage in forward and reverse fluid flow applications.
Some known bidirectional sealing assemblies include spacer rings to maintain opposing seals separated or spaced apart from each other. The spacer rings are often sized to provide a clearance between the spacer ring (e.g., an outside diameter of the spacer ring) and a surface of the cage (e.g., an inner surface of the cage). However, due to wear, manufacturing tolerances, etc., the spacer ring may engage or contact the surface of the cage as the valve plug moves between an open position and a closed position, thereby increasing friction between the closure member or the seal assembly and the cage. While spacer rings made of metal material can be used to prevent excessive or rapid wear of the spacer rings, such metal spacer rings may mare or damage the cage surface, thereby causing unwanted leakage and reducing the life of the cage.